Rare Species Guide

  Synonyms

Spiranthes casei

  Basis for Listing

Our knowledge of Spiranthes casei var. casei (Cases ladies’ tresses) has a rather unusual history. It was not recognized as a distinct species until 1974, when it was separated from the S. cernua (nodding ladies' tresses) complex (Catling and Cruise 1974). And it was not known to occur in Minnesota until 2000, when it was discovered near Hibbing by Rolf Dahle and Audrey Engles. These two volunteer botanists eventually found it at five distinct locations, all within a distance of about 40 km (25 mi.) of each other (Laurentian Mixed Forest Province) (Smith 2012). As of 2015, these five locations are the only known occurrences in Minnesota.

All the habitats where S. casei var. casei occurs in Minnesota are associated with iron ore and taconite mines. These habitats are not stable in either an ecological sense or a land use sense; and their future is uncertain. In truth, these may not be the only locations where S. casei var. casei exists in Minnesota. Undiscovered populations, if any exist, may be more secure than the ones we presently know about. However, based on current information, the future of S. casei var. casei in Minnesota is precarious at best. The small number of occurrences of this plant in Minnesota, and the vulnerability of those occurrences, led to S. casei var. casei being designated a threatened species in 2013.

The seemingly superfluous appellation “var. casei’” for plants found in the Great Lakes region (including Minnesota) is necessary to distinguish it from “var. novaescotiae” (Nova Scotia ladies' tresses), which is a smaller variety restricted to southern Nova Scotia (Sheviak and Brown 2002).

  Description

Spiranthes casei var. casei is 14-38 cm (5.5-15 in.) tall; the stem arises from a descending cluster of 2-7 fleshy tuberous roots. There are 2-5 leaves clustered on the lower portion of the stem; the lowermost is ovate-lanceolate, 5-10 cm (2-4 in.) long, 1-2 cm (0.4-0.8 in.) wide, and withers at anthesis; the middle leaves persist through anthesis, are linear-lanceolate to oblanceolate, 10-20 cm (4-8 in.) long, and 0.5-1.0 cm (0.2-0.4 in.) wide; the uppermost leaves decreasing in size until they grade into the bracts. The inflorescence is a terminal spike, 5-12 cm (2.0-4.7 in.) long, with 14-35 flowers arranged in a single vertical column, spiraled 3-6 times; each flower is subtended by an ovate-lanceolate bract, 7-15 (20) mm (0.3-0.6[0.8] in.) long. The flowers are ivory to yellowish white and strongly nodding; the perianth is 5.5-8.0 mm (0.20-0.23 in.) long; the sepals are creamy white to greenish white, lanceolate, obtuse, and 5-7 mm (0.2-0.3 in.) long; the lateral sepals are appressed; the petals are similar to the sepals; the floral lip is ovate to ovate-oblong, often darker centrally, 5.0-7.5 mm (0.2-0.3 in.) long, 3-5 mm (0.1-0.2 in.) wide; the apex is truncate. The seed capsules are ascending to erect, 5-8 mm (0.2-0.3 in.) long. Flowering occurs from August 20 to September 15, perhaps peaking the first week in September (Smith 2012).

When compared to S. cernua (nodding ladies’ tresses), the species most likely to be confused with S. casei var. casei, the lower leaves are noticeably shorter and broader; however, the lower leaves may be gone by the time the flowers appear. The flowers themselves are different in a number of subtle ways.  They are measurably smaller and appear more “closed” than those of S. cernua, meaning the sepals and petals do not flare out as much, and they are not pure white like S. cernua, they are creamy white or yellowish white. Also, the spike of S. casei var. casei is a single, vertical column of flowers, in a gentle spiral. The spike of S. cernua has 2 or more vertical columns, twisted into a tight spiral. Be sure to check all the plants in any population of S. cernua found in the northeast, you may have a mixed-species population containing S. casei var. casei (Smith 2012).

  Habitat

All five known locations of S. casei var. casei are in drained sediment basins on the iron range in Itasca and St. Louis counties; it has been found nowhere else in Minnesota. The basins are typically hundreds of acres in size and were created by the construction of tall earthen dikes for the purpose of disposing of the mineral residue, called "tailings", of iron ore and taconite mining. The tailings are carried to the basins in a slurry of water. Over a period of years, the basins become filled with water, and the tailings settle out to the bottom. Then the water is drained, leaving a basin filled with a fine-textured reddish material, the mineral residue of mining. In some cases, the basins were planted with trees or grasses in an act of reclamation, usually with poor success; otherwise, they were left to revegetate on their own (Smith 2012). 

In time, the basins were colonized by common plants from adjacent habitats. After a period of perhaps 20 or 30 years, a young forest typically developed (northern mesic mixed forest), with scattered stands of Populus tremuloides (trembling aspen), Populus balsamifera (balsam poplar), Betula papyrifera (paper birch), and Alnus incana (speckled alder). There are also a variety of grasses, sedges, and forbs, mostly native forest species or early successional generalists as well as several species of nonnative weeds. At some point in this process of reforestation, the basin becomes very attractive to S. casei var. casei and a variety of other native orchid species.

How S. casei var. casei arrived in Minnesota is uncertain; however, it likely arrived as wind-borne seeds, which is how orchids generally disperse from one area to another. But the surprising aspect is how quickly it happened, and how consistently it was repeated from one basin to another. This is not a fluke; it happened at least five times over the past 30-40 years. The only conclusion is that there must be an awful lot of orchid seeds floating on the wind currents, and orchid seeds must be extremely good at exploiting suitable habitat when they find it.

Although the exact circumstances of S. casei var. casei in Minnesota may be unique, the habitats reported in other states and Canadian provinces are not too dissimilar. They are described variously as rocky hills, outcrops, borrow pits, dry to moderately moist acidic soils, meadows, pine barrens, and open woodlands (Sheviak and Brown 2002; Reddoch and Reddoch 1997). In many important ecological aspects the sediment basins in Minnesota, in spite of their human origin, closely resemble the natural habitats where S. casei is found elsewhere; perhaps we should not be too surprised that S. casei var. casei found them.

  Biology / Life History

Species in the genus Spiranthes (laidies' tresses) have no corm, bulb, or obvious rhizome below ground. The stem appears to arise directly from the top of a cluster of rather stout fleshy roots. The roots seem to function as food storage organs, much as a tuber might; hence, they are often called “tuberous roots”. The sequence of growth is not entirely clear, but it appears that each root continues to grow for perhaps two years then begins to fade and shrivel. By autumn of its third year, the old root is replaced by a new root, produced at the base of the stem above the old root. There is a constant turn-over of roots, with each plant having 2-7 functional roots at any given time. Species of Spiranthes in general tend to mature quickly from seed but do not live long, rarely as long as 10 years (Ames 1921; Anderson 1991; Antlfinger and Wendel 1997).

Long-tongued bees, such as bumblebees, probe flowers for the nectar secreted into the base of the flower. In the process, they pick up pollinia on their eyes or mouthparts and transfer them to other flowers (Catling and Catling 1991; Catling 1983). It seems that S. casei var. casei can also produce viable seed without pollination (Catling 1982). This happens through the process of agamospermy (asexual reproduction in which seeds are produced from unfertilized ovules), a rare process among North American orchids.

  Conservation / Management

Because of the unique habitat situation involving S. casei var. casei in Minnesota, management recommendations cannot be suggested at this time. However, it is of the utmost importance to find a population occurring in a more natural habitat that would have more potential for long-term management.

  Best Time to Search

The best time to search for S. casei var. casei is when the flowers are fully developed, which usually occurs from August 20 to September 15, perhaps peaking the first week in September (Smith 2012).

  Authors/Revisions

Welby Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Ames, O. 1921. Notes on New England orchids: 1. Spiranthes. Rhodora 23:73-85.

Anderson, A. B. 1991. Symbiotic and asymbiotic germination and growth of Spiranthes magnicamporum (Orchidaceae). Lindleyana 6:183-186.

Antlfinger, A., and L. Wendel. 1997. Reproductive effort and floral photosynthesis in Spiranthes cerna (Orchidaceae). American Journal of Botany 84(6):769-780.

Catling, P. M. 1982. New combinations for forms and varieties of some North American orchids. Naturaliste Canadien 109(2)277-278.

Catling, P. M. 1983. Autogamy in eastern Canadian Orchidaceae: a review of current knowledge and some new observations. Naturaliste Canadien 110:37-53.

Catling, P. M. 1983. Pollination of northeastern North America Spiranthes (Orchidaceae). Canadian Journal of Botany 61(4):1080-1093.

Catling, P. M., and J. E. Cruise. 1974. Spiranthes casei, a new species from northeastern North America. Rhodora 76:526-536.

Catling, P. M., and V. R. Catling. 1991. A synopsis of breeding systems and pollination in North American orchids. Lindleyana 6(4):187-210.

Hapeman, J. R. 2009. Orchids of Wisconsin: an interactive flora [web application]. Spiranthes casei Catling & Cruise. <http://www.botany.wisc.edu/orchids/casei.html>. Accessed 27 May 2009.

Minnesota Department of Natural Resources. 2003. Field guide to the native plant communities of Minnesota: the Laurentian mixed forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 352 pp.

Reddoch, J. M., and A. H. Reddoch. 1997. Orchids in the Ottawa District: floristics, phytogeography, population studies and historical review. The Canadian Field-Naturalist 111(1):1-24.

Sheviak, C. J., and P. M. Brown. 2002. Spiranthes. Pages 530-546 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 26. Oxford University Press, New York, New York.

Smith, W. R. 2012. Native orchids of Minnesota. University of Minnesota Press, Minneapolis, Minnesota. 400 pp.